This invention relates generally to spot drilling and countersink tools and more particularly to a novel combined spot drill and countersink tool having a replaceable indexable insert.
In metal working applications spotting and centering drills are used to very accurately locate holes within close tolerances, for example within 0.000 to 0.002 inches of true centerline position on CNC and similar drilling machines. The spot drills provide a true center position from which longer twist drills may locate and thereafter drill deep straight holes in all types of materials. In the past spotting and centering drills have been made of one piece from high speed steel material or solid carbide material and drill point angles and flutes are ground in one end of the material as required.
Such conventional spotting and centering drills are disadvantageous in several respects. First, the drill point must be reground periodically and this requires removal of the drill from its holder. When the spot drill is reinserted into its holder after sharpening, the position of the drill and/or its holder must be reset lengthwise to ensure that a spot of proper depth is attained. Second, because of the high cost of the solid carbide drills the high speed steel spot drills are more commonly used, but these have severe limitations as to the speed at which they are capable of spot drilling. Thus, quite often the high speed steel spot drills are used to save cost but at a substantial sacrifice in drilling speed.
Conventional countersink and deburring tools are used to debur, chamfer and/or countersink the outermost ends of already drilled holes on a face of a part and thereby provide an angled surface of 60, 82 or 90 degrees of desired depth. The angled surface may simply serve to debur the edge, provide a thread chamfer, or be deep enough to receive the head of a bolt. Countersink and deburring tools have traditionally been made of one piece material but in more recent years have been provided with indexable replaceable inserts by which the already formed hole is enlarged. Prior U.S. Pat. Nos. 4,197,042, 4,293,254, 4,505,626 and 4,591,302 illustrate countersinking tools having removable inserts.
However, existing countersink tools, whether they be of the one piece solid material type or of the type having replaceable inserts, will not spot drill to provide an accurate center point for a subsequent drilling operation. The countersink tools can only enlarge the diameter of an already formed hole.
It has also been proposed to provide other type drills with replaceable inserts, for example, the spade drills illustrated in U.S. Pat. Nos. 4,047,826, 4,060,335 and German Pat. DE 2056091. However drills of this type are not capable of spot drilling or spot facing within the tolerances normally required for such an operation, but are usually employed in rough drilling deep holes where accuracy is not required. Similarly U.S. Pat. No. 4,527,931 illustrates a mining drill having a replaceable insert used for drilling coal mine bolt holes, another application in which accuracy is not important.